The invention relates to an electromagnetic hydraulic valve as well as a method of its production. The electromagnetic hydraulic valve is especially beneficial for use with proportional valves for controlling of a device for adjusting the rotation angle of a camshaft relative to the crankshaft in an internal combustion engine.
From DE 198 53 670 A1 a category-defining proportional valve for the controlling of a device for adjusting the rotational angle of a camshaft relative to the crankshaft of an internal combustion engine is provided, which consists essentially of a cylindrical hollow electromagnet with an armature which moves in it axially, and of a cylindrical valve housing with an axial bore, and a piston valve set in it. The piston valve, which is designed as a hollow piston, is set with the armature of the electromagnet, in such an interaction by means of a valve push rod that the magnetic attraction axially moving the armature when the current feed is applied to the electromagnet, is transmitted to the piston valve and shifts it axially in the fixed axial bore of the valve housing against the force of a compression spring. Furthermore, the valve housing comprises in on a periphery thereof three annular grooves axially spaced from each other, in which several equally distributed radial openings are configured, which open into the axial bore of the valve housing. Above the radial bores as well as above the one-sided open bore in the valve housing there is a proportional valve with a pressure connection, tank connection and two consumer connections in the air connection, by means of which the in- and outflow of the hydraulic medium to and from the pressure chambers of the device used to adjust the rotation angle of a camshaft is controlled. The respective rate of flow is thereby adjusted by means of two annular control sections at the ends of the piston valve which in accordance to the current feed of the electromagnet and the axial position of the piston valve release a part of the opening cross section of the radial bores of the consumer connections and therefore alternatively connect the pressure connection and the tank connection to one of the consumer connections. At the same time, the control sections of the piston valve and the gutters of the valve housing, which originate between the individual radial bores of each consumer connection, create a guide for the piston valve within the axial bore of the valve housing, by means of which a seizure of the piston valve in its axial displacement is therefore avoided.
Proportional valves designed in such a way show this undoubtable advantage that the control sections of the piston valve are at the same time also its bearing surfaces in the axial bores of the valve housing and in this way both the piston valve and the valve housing have a relatively short face-to-face length. But this faces the disadvantage that at least the radial bores in the valve housing, which belong to the consumer connections, because of their overall relatively small opening cross section surface make possible only a low flow of hydraulic medium through the valve and moreover because of the semicircular forms of the opening cross section of these radial bores the flow of the hydraulic medium through the valve in the individual positions of the piston valve is not linear to the respective position of the armature of the electromagnet. When such a proportional valve is applied for the controlling of a device for adjusting the rotational angle of a camshaft, it implicates on the one hand that the valve has a large internal hydraulic resistance, which is expressed in a high pressure drop on the consumer connections and at least in case of devices with a relatively high intake capacity it implicates that their maximum rate of change remains under a permitted minimum face value. On the other hand the non-linear flow through the valve has the effect that the adjustment pressure, which is necessary for a fast adjustment process, takes place in each pressure chamber of the device relatively late because the linear control sections of the piston valve open the round radial bores of the consumer connections first only at the bore edge with a minimum opening cross section until the opening cross section is larger and larger by way of following the axial movements of the piston valve and then in the final position the necessary adjustment pressure is reached. Furthermore, the radial bores in the valve housing have also proved to be disadvantageous regarding the production process because the exact bore of the radial borings is very time consuming and cost-intensive and moreover requires laborious subsequent machining to remove the splinters and ridges.
There are already several solutions known to avoid these disadvantages in which the proportional valve, similar to the solution revealed in DE 100 51 614 A1, has a piston valve in the valve housing, which is led on the radial surfaces of two additional guides in the axial bores set on the ends of the piston valve. Those additional guides on the piston valve make it possible that the control sections of the piston valve do not need to undertake any leading functions and therefore can be freely accommodated by rotating versus two annular grooves in the axial bore of the valve housing. Both of those annular grooves are laterally limited by two piston lands and each of them is connected through a large surfaced one-sided radial opening in the valve housing with the consumer connections. The piston lands of those annular grooves interact here with the control sections of the piston valve in such a way that in accordance with the current feed of the electromagnet and the axial position of the piston valve connected with that a complete circular opening cross section is released to the annular grooves and with that the pressure connection and the tank connection is connected alternatively with the consumer connections.
As a result the advantage of such a designed proportional valve is provided first of all in the relatively large, circular opening cross section surface in each position of the piston valve, which enables a high and moreover linear compared to the displacement of armature of the electromagnet flow of hydraulic medium through the valve, and consequently assures fast adjustment processes in a device for the adjustment of the rotational angle of the camshaft. But a disadvantage must be accepted that the piston valve has a relatively large face-to-face length, which is caused by the additional guides that therefore, correspondingly, a long valve housing also needs deep inserting bores. Furthermore, because of the one-sided design of the radial openings in the valve housing both to the consumer connections as well as to the pressure and tank connection such a proportional valve needs an exact emplacement position and is therefore applicable only in correspondingly designed connecting lines.